SPADA Draft Documents

highly biased and not recommended for most purposes. Judgement samples should be 338 reserved for instances when the individual collecting the sample is only using the sample 339 as a source of soil microbes. 340 From a statistical perspective, simple random samples are more representative of an 341 area than judgement samples as each sample has an equal opportunity to be selected. A 342 common technique for collecting simple random samples is to establish a grid consisting 343 of two sets of parallel lines at right angles to each other. Each line is assigned a unique 344 number. Pairs of numbers are drawn from a random number table and used to establish 345 intersecting points that denote where a sample will be collected. This process is repeated 346 until the number of required samples is reached. Another simple random sample method 347 is to use a pair of random numbers to designate a distance and angle from a selected 348 starting point. 349 Stratified random sampling is similar to simple random sampling except that the area 350 of interest is divided into smaller sub-areas. These sub-areas are selected based on known 351 variations in the soil or other factors of interest. Samples are collected within each sub- 352 area in a random manner as described above. The advantage of stratified random 353 sampling is that a researcher can compare results between the sub-areas and possibly 354 correlate results to the factor of interest. 355 Systematic sampling is comprised of sampling at predetermined points or intervals, 356 such as points along parallel lines or intervals based on the distance from a point. This 357 type of non-random sampling is performed in order to ensure an area is well understood. 358 Systematic sampling is useful for sampling after an outdoor activity with the sampling 359 lines informed by the activity and its location. 360

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